What Determines Whether a Formed Part's Flange Should Get a Hem Instead of a Plain Edge?

A hem earns its place when the raw edge itself is the problem: an edge that gets handled, faces a sealing surface, or needs stiffness without added gauge. If none of that applies, a plain edge is cheaper and easier to hold flat.

What a hem actually buys you

A hemmed flange folds the sheet back on itself, usually flat or with a small closed gap, so the sharp cut edge ends up tucked inside the fold instead of exposed. Two things follow. The edge a hand or a gasket contacts is now a rounded fold instead of a cut edge. And the doubled-over section is noticeably stiffer than the same single-thickness flange. That second point matters more than people expect. A hem is a cheap way to add rigidity to a panel edge without going to heavier gauge across the whole part, which would change weight, forming tonnage and every other flange dimension.

Where it makes sense

Enclosure panels with an edge a hand will pass over are the obvious case. A raw laser-cut edge on cold rolled or galvanized steel is genuinely sharp, and a hem removes that without a secondary deburring pass. Edges that seat against a gasket or another panel benefit the same way, presenting a smooth folded surface instead of a cut edge with kerf taper that varies part to part. And panels that oil-can along a free edge often just need the stiffness a hem adds, cheaper than bumping the whole part to heavier gauge.

Where it doesn't

A hem costs an extra bend, extra flat pattern length to fold back on, and a decision about how tight the closed gap should be. Tight hems risk cracking at the fold, especially in stiffer tempers or thicker material, the same risk you'd see on any tight-radius bend. If the edge is internal, gets covered by another part, or never gets handled, a hem is just added cost for no functional benefit. Plain edges are also easier to hold flat through forming, since there's no doubled-over section pulling unevenly as the part comes out of the die.

Material and thickness change whether it's a good idea at all

Thicker stock and harder tempers need a bigger hem radius to avoid cracking at the fold, eating into the flat pattern in a way thin, soft aluminum won't. Choosing between 5052 and 6061 for a part that's going to get hemmed should factor that crack risk in up front, not get discovered on the first production run.

The takeaway

Ask what the edge is actually for before deciding. Handled, sealed against, or needs stiffness: hem it. Tucked away and never touched: leave it plain, save the bend. DigiForge forms cold rolled steel, galvanized steel, 5052 and 6061 aluminum, and 304 and 316 stainless with a ±0.5° bend angle tolerance, from STEP, STP or DXF files, on a 2-week standard lead time. Call out the hem radius on the drawing so it doesn't get guessed at on the floor.